Dean - He's a nurturer, but he's lazy. And cheap. So instead of medical school, he gets night classes and RN certification. He's also the perfect choice to care for a kid.

Sam - I checked my e-mail and I had ER doc at first. He's smart, capable, but makes hasty decisions - perfect for the chaos of the ER. And if mistakes happen... well, he just keeps rushing headlong. In the chaos, it's easy to sneak out things like drugs with no one noticing and he can hide it very well.

Anna and Cas - Since surgeons like to play God, the angels are surgeons. Anna's always been the feeling type, falling to feel, feeling protective of the Winchesters and then the entire world... she's all about heart, this gal. And Cas, until he really saw what was going on, he was all about the logic, the orders and the rules. Stuck in his head, that one, so I stuck him in everyone else's.

Jo - She's dead back home, not quite an angel, but she's not human anymore, so she's the in-between. The rookie, the learner. Which was also her role in the show, learning from San and Dean, hunting with her mother, just about solo, not quite.

See? I THOUGHT ABOUT IT.